1. Field of Invention
This invention relates generally to medical instruments provided with means to illuminate the field of medical interest, and more particularly to a disposable medical instrument and light pipe illumination assembly fabricated of synthetic plastic material.
Though the invention will be described mainly in the context of medical, surgical and dental applications, it is to be understood that the invention is not limited thereto, for an assembly in accordance with the invention is capable of transmitting light of high intensity by means of a flexible light pipe to remote or inaccessible work sites which are difficult to illuminate by conventional techniques.
The invention, as it relates to improvements in light pipes, is useful in a broad spectrum of industrial applications to carry out such functions as sensing and controlling, as well as general illumination. It is also useful in providing warning or personal safety lights to be mounted on bicycles or other vehicles, or to be worn on the person.
The professional concern of doctors, surgeons and dentists is with body cavities and surgical sites which, unless clearly visible, cannot be properly diagnosed or treated. Existing techniques for illuminating such regions are often inadequate and unsafe, for they either do not succeed in supplying sufficient illumination or they generate excessive amounts of heat which may injure human tissue as well as cause discomfort to the observer. In some instances, commercially available illuminators interfere with medical procedures and also constitute a hazard to both patient and doctor.
The standard operating room illuminator is constituted by batteries of explosion-proof spot lamps and floor lamps, which are capable of being shifted or aimed to suit particular procedures. Such illuminators, which are quite costly, are not only cumbersome, but they fail to afford adequate illumination for deep cavities, in that the light sources are above or behind the surgeons or other operating personnel, whose heads, hands and instruments, as they shift position, often block the light rays.
In recent years, attempts have been made to use long, flexible fiber optics light guides in medical and related applications. Such guides are advantageous in that they furnish "cold light" and segregate the heavy and bulky assembly of lamp, condenser and cooling system from the point of observation. Also, with the development of flexible fiber optic guides with fused ends and plastic casings, sterilization of the instrument is possible.
In its preferred form, the present invention involves a medical instrument associated with a flexible light guide in a monofilament-core pipe format, this representing a particular species of an optical fiber. It is important, therefore, that the distinctions which exist between a conventional multi-fiber optical light pipe or cable and a light pipe having a monofilament-core be clearly understood.
An optical fiber is a dielectric waveguide structure which functions by internal reflection to confine and guide light. It consists of an inner dielectric material, called the core, surrounded by another dielectric material having a smaller refractive index, referred to as the cladding. Currently, all optical fibers in general use have a cylindrical circular cross section.
The amount of light flux which an optical fiber is capable of conveying depends on the cross-sectional diameter of the core; and when there is a need to transmit large amounts of light at a constant level for purposes of illumination, rather than a modulated light signal for purposes of communication, use is usually made of a bunched cluster of optical fibers, each conveying a small amount of light.
Since the present invention is concerned primarily with illumination, it employs in conjunction with a medical or other work instrument a light guide in the form of a flexible pipe having a monofilament-core of large diameter surrounded by a cladding tube. The monofilament core serves the same function as a cluster of small diameter cores, but operates with far greater optical efficiency to transmit large amounts of light with minimal transmission losses, and it also is more bendable than conventional multi-filament core light pipes.
Fiber optic guides may be used as auxiliary illuminators for close diagnostic and surgical operations, as illuminators for direct or indirect ophthalmoscopes, and as specially shaped illumination accessories to classical-designed cystoscopes, proctoscopes, retractors, and various forms of medical, surgical and dental tools.
Despite the obvious advantages of fiber optics for coldlight illumination, their use in the surgical, medical and dental fields has been relatively limited. The reason for this does not lie in any inherent theoretical deficiency, but in the fact that with existing technology, the three basic components of the fiber optics system, when brought together, do not afford sufficient illumination in those situations calling for large amounts of cold light which can be readily directed to selected regions of a body cavity.
But apart from the limitations of existing multi-fiber light pipes is the fact that with heretofore known combinations of light pipes and medical instruments, both the instrument and the light pipe have to be cleaned and sterilized after each use to render them suitable for reuse, for the high costs of these assemblies do not permit their disposal after a single use. Such post-operative processing militates against the practical value of the combination.
Thus in the 1982 brochure entitled "Fiberoptics for Surgery," published by Applied Fiberoptics, Inc., a company affiliated with Codman & Surtleff, Inc., of Randolf, Mass. (Codman), there is illustrated a stainless steel "Britetrac" retractor associated with a fiber optic bundle to deliver cool illumination to the surgical field.
According to the Codman brochure, the "Britetrac" instrument lends itself to processing in ultrasonic washers to avoid tedious hand cleaning. But then the instrument, including the fiber optic bundle, must be sterilized in an autoclave or by other acceptable means.
Another serious limitation of the Codman "Britetrack" instrument is that the light emitted from the outlet of the light pipe is on a fixed axis, and the surgeon, in the course of an operating procedure in which the retractor position remains unchanged, must alter the orientation of the light input in order to better illuminate, say, a deep recess in the surgical site which is not in line with the outlet. While the surgeon could then instruct an assistant to adjust the overhead lights to supply more light to the recess, his assistant may then not be free to make this adjustment; or if he is free, he may not understand what the surgeon has in mind.
A highly significant advantage of the present invention is that the outlet end is readily orientable by the surgeon himself who may redirect the light from time to time toward any region of interest. And because the invention lends itself to combining several light pipes with a single instrument, each pipe outlet may be oriented differently by the surgeon to afford a highly versatile illumination capability.
2. Prior Art
The prior art patent of greatest interest is the Reick-Wilder U.S. Pat. No. 3,641,332, which discloses a flexible light pipe constituted by a monofilament core of resinous material of large diameter, such as methyl methacrylate contained within a cladding tube formed of FEP (Teflon), the core being separated from the tube by a film of air.
As pointed out in this patent, the ideal light guide has a core of the highest possible refractive index in combination with a cladding of the lowest possible refractive index. Commercially-available light pipes, such as the "CROFON" pipe made by duPont, falls far short of this ideal, for this pipe makes use of a polymethyl methacrylate core in a polyethylene cladding tube.
Polyethylene has a refractive index of 1.54, as compared to air, whose index is 1.0. However, though air has the lowest possible refractive index, air normally cannot serve as a cladding, for, if unconfined, it is incapable of protecting the core from scratches and contamination which degrade its quality. In the Reick-Wilder light pipe, one still has a protective plastic outer tube; but it is the inner air film, except at those limited points where the core makes physical contact with the tube, which acts effectively as a cladding having the lowest possible refractive index. At those points where the core touches the Teflon tube, internal reflection will still take place, for Teflon has a refractive index of about 1.34 which is lower than that of the core and therefore functions as a cladding, though this cladding is less effective than air.
Also pertinent to the present invention is the Wilder-Kanbar U.S. Pat. No. 3,729,006, which discloses a hand-held surgical retractors fabricated of light-weight, glare-free, synthetic plastic material.
The Wilder-Kanbar patent spells out the many advantages gained by the use of a plastic retractor over conventional, relatively heavy and expensive stainless steel retractors. But in the context of the present invention, the greatest value of the all-plastic retractor is that it can be combined with an all-plastic light pipe to create a unit that is low-cost and disposable, thereby obviating the need for post-operative cleaning and sterilization procedures. These procedures are time-consuming and require hospital personnel for this purpose. When one considers the total cost of processing a unit so that it can be reused in a surgical procedure, little is lost in discarding the inexpensive, all-plastic unit and using a fresh unit in the next procedure.